linux/include/uapi/linux/sched/types.h

/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
#ifndef _UAPI_LINUX_SCHED_TYPES_H
#define _UAPI_LINUX_SCHED_TYPES_H

#include <linux/types.h>

#define SCHED_ATTR_SIZE_VER0 …
#define SCHED_ATTR_SIZE_VER1 …

/*
 * Extended scheduling parameters data structure.
 *
 * This is needed because the original struct sched_param can not be
 * altered without introducing ABI issues with legacy applications
 * (e.g., in sched_getparam()).
 *
 * However, the possibility of specifying more than just a priority for
 * the tasks may be useful for a wide variety of application fields, e.g.,
 * multimedia, streaming, automation and control, and many others.
 *
 * This variant (sched_attr) allows to define additional attributes to
 * improve the scheduler knowledge about task requirements.
 *
 * Scheduling Class Attributes
 * ===========================
 *
 * A subset of sched_attr attributes specifies the
 * scheduling policy and relative POSIX attributes:
 *
 *  @size		size of the structure, for fwd/bwd compat.
 *
 *  @sched_policy	task's scheduling policy
 *  @sched_nice		task's nice value      (SCHED_NORMAL/BATCH)
 *  @sched_priority	task's static priority (SCHED_FIFO/RR)
 *
 * Certain more advanced scheduling features can be controlled by a
 * predefined set of flags via the attribute:
 *
 *  @sched_flags	for customizing the scheduler behaviour
 *
 * Sporadic Time-Constrained Task Attributes
 * =========================================
 *
 * A subset of sched_attr attributes allows to describe a so-called
 * sporadic time-constrained task.
 *
 * In such a model a task is specified by:
 *  - the activation period or minimum instance inter-arrival time;
 *  - the maximum (or average, depending on the actual scheduling
 *    discipline) computation time of all instances, a.k.a. runtime;
 *  - the deadline (relative to the actual activation time) of each
 *    instance.
 * Very briefly, a periodic (sporadic) task asks for the execution of
 * some specific computation --which is typically called an instance--
 * (at most) every period. Moreover, each instance typically lasts no more
 * than the runtime and must be completed by time instant t equal to
 * the instance activation time + the deadline.
 *
 * This is reflected by the following fields of the sched_attr structure:
 *
 *  @sched_deadline	representative of the task's deadline
 *  @sched_runtime	representative of the task's runtime
 *  @sched_period	representative of the task's period
 *
 * Given this task model, there are a multiplicity of scheduling algorithms
 * and policies, that can be used to ensure all the tasks will make their
 * timing constraints.
 *
 * As of now, the SCHED_DEADLINE policy (sched_dl scheduling class) is the
 * only user of this new interface. More information about the algorithm
 * available in the scheduling class file or in Documentation/.
 *
 * Task Utilization Attributes
 * ===========================
 *
 * A subset of sched_attr attributes allows to specify the utilization
 * expected for a task. These attributes allow to inform the scheduler about
 * the utilization boundaries within which it should schedule the task. These
 * boundaries are valuable hints to support scheduler decisions on both task
 * placement and frequency selection.
 *
 *  @sched_util_min	represents the minimum utilization
 *  @sched_util_max	represents the maximum utilization
 *
 * Utilization is a value in the range [0..SCHED_CAPACITY_SCALE]. It
 * represents the percentage of CPU time used by a task when running at the
 * maximum frequency on the highest capacity CPU of the system. For example, a
 * 20% utilization task is a task running for 2ms every 10ms at maximum
 * frequency.
 *
 * A task with a min utilization value bigger than 0 is more likely scheduled
 * on a CPU with a capacity big enough to fit the specified value.
 * A task with a max utilization value smaller than 1024 is more likely
 * scheduled on a CPU with no more capacity than the specified value.
 *
 * A task utilization boundary can be reset by setting the attribute to -1.
 */
struct sched_attr { … };

#endif /* _UAPI_LINUX_SCHED_TYPES_H */